Arrangement of DNA and histones in the 100A chromatin fiber will be studied using embedding in thick negative stain, with the hydration stage and frozen within the cold stage of the Million Volt electron microscope. The folding or coiling of the 100A fiber to form the 200A chromatin fiber of native nuclei will be investigated. The arrangement of the 200A fiber in chromomeres of Drosophila polytene chromosomes will be studied. Specific bands including the brightly fluorescent Quinacrine stained bands will be compared. Chromosome condensation during mitosis and meiosis will be studied using the high voltage EM with regard to changes in the three dimensional pattern of 200A fibers and their relation to the chromonema seen by light microscopy.